SpaceX made international headlines this May when their Crew Dragon spacecraft blasted into orbit aboard a Falcon 9 rocket, carrying astronauts Doug Hurley and Bob Behnken to the International Space Station. But what some astute viewers may have noticed during liftoff is that Crew Dragon did not have a traditional launch escape system (LES) tower on top of its nose cone.
So, what is the emergency exit plan for astronauts during a failed Crew Dragon launch? And how do the LES of other commercial spacecraft work?
Abort!
LES towers, first designed by Maxime Faget, have been employed since the 1960s. They depend on escape rockets — typically utilizing solid propellant — that quicky lift the spacecraft away from what is presumed to be an exploding rocket. These escape rockets then carry the spacecraft to a safe altitude for parachute deployment before separating from the crew capsule.
Instead of an LES, Project Gemini used a highly controversial ejection seat system that violently threw astronauts away from the booster in the event of an emergency. But Mercury and Apollo astronauts both trusted LES towers, as well as the Russian Soyuz and Chinese Shenzou programs.
SpaceX: Escaping Crew Dragon
Elon Musk’s SpaceX has proven to be nothing if not innovative. While recognizing that crewed spacecraft must have an escape system, SpaceX has gone in a different direction with their LES. The Crew Dragon has eight SuperDraco engines incorporated into the body of the spacecraft itself, none of which utilize an external tower.
In a further break from tradition, the SuperDraco engine utilizes liquid propellants, which are more controllable than solid propellants. These storable, stable liquid propellants are the hypergolic agents monomethylhydrazine and dinitrogen tetroxide, with the latter functioning as the oxidizer. These propellants do not need an external ignition source. Hypergolic fuels ignite on contact with each other, further simplifying the design of the engine — and, of key importance, allowing the engine itself to be restarted.
Engines that use hypergolic fuels have been shown to be extremely reliable (the Apollo Service Module’s engine used hypergolic fuel, as did the Lunar Module’s descent and ascent engines). But to prove they were ready for crewed flights of Crew Dragon, SpaceX performed a full launch abort test of their spacecraft on January 19. 2020, intentionally destroying a Falcon 9 rocket in the process.
Blue Origin: Escaping New Shepard and New Glenn
Blue Origin, another private spacecraft venture funded by Amazon founder Jeff Bezos, is not as far along in terms of development as SpaceX, but they are making undeniable progress. Blue Origins program currently has two spacecraft in development: the suborbital New Shepard (a reference to Alan Shepard’s suborbital Freedom 7 flight) and the orbital New Glenn (a reference to John Glenn’s orbital Friendship 7 fight).